The current threads about batteries got me thinking. I have an 07 MC X45. Stock set up electrically speaking. I have to replace one of these batteries probably on average every season. I have replaced the battery with an equivalent to the stock batteries which says 24M on the top of them The ones I have in there now are made by Xtreme and they are labeled as a marine starting battery. This is what they gave me when I take one in to have it replaced by Batteries Plus. Is this bad luck, bad habits, or cheap batteries. A friend tells me it's due to the constant hard jolts of hitting double ups that leads to their short life spans. I know when one is going bad, because it gets warm and starts to stink super bad. I had my alternator checked and the mechanic says it tests out fine...any ideas? I don't know anything about batteries, alternators, etc.

24M is the group size of the battery. Group 24 is probably the most common size put into boats from the factory/dealer. There should be a tag with the actual part number. If there is a DC somewhere in there it is a deep cycle battery. If DP it is a dual purpose similar to the an interstate SRM battery.

How are your batteries wired?

What exactly is your system made up of?

Do you cove party and/or listen to the stereo at high volumes while not driving?

In what way are the batteries failing, shorting out as in a broken plate, dead cell or just not holding a full charge. Are they being found dead come spring? Do you use any kind of charger off season or during?

How the batteries are used and maintained typically has more to do with its life span then its brand or type.

The battery you use to start your boat should be a 'starting' type battery. This type is designed to allow a lot of current flow as necessary for cranking the starter. Batteries used for stereo and accessories are usually better if they can handle a deeper 'cycle' but don't need to flow high amps. The deep cycle means being drawn down low and then recharged fully. Using a battery differently than it is designed for can contribute to a shorter life.
What one starts to stink and get hot it probably has an internal short that could be caused be a plate breaking or by material flaking off the plates and falling to the bottom. Both of these can be caused by vibration or impact loads. Some batteries are designed specifically for abuse like this.
Answer Brett Yates's questions and we'll know more about your needs.

Brett T. You probably saw my other post in the battery thread, so this may be a repeat. As Art is probably totally correct, I am doing it completely wrong in my boat. I use 2 sealed 2000amp audio deep cycle batteries (kinetic HC2000) and put them on a perko. They both are used as starting batteries and to run my system (simple system, 1000w amp, 6 in boats and a 12" sub.. no tower speakers). I have had them since 2008 with no problems and I rarely tend them (only a few times in winter months when not in use, I have gone at least 2 or 3 winters without tending/charging them)

maybe I am just lucky, but i spent about $450 for both batteries and someday, when I eventually kill them, I will buy 2 more. I like that they are sealed and do not bulge or leak or corrode, and you can mount them in any direction.

The boats stock. Two batteries wired together with a perko switch. Stock stereo, factory, 4 tower speakers, two amps, two subs. I added one sub that is not factory JL. I go out to ride. However, certain days we will float with the engine off listening to the stereo, but never at high volumes. I typically remove the batteries and store inside during the winter. Some years ill remember to charge them a little bit during the winter, some i don't.. I am told they are starting batteries. I always know when one goes bad because it starts to stink so bad while i am out on the water.

A battery that heats up is a liability and isn't doing your alternator any favors. If it's swelling and stinking it accepts current but will never fully charge and the minimal charge will quickly dissipate.
Measure the level of depletion on your new battery with a voltmeter at the battery terminals after a period at rest. Have enough battery capacity that you are not going below 50% (12.0 volts). If you are then add another battery to the stereo bank side. But do this before you have any real wear and tear on the battery since two batteries in parallel or series on the same bank should be identical to begin with in every sense.
Use nothing but a deep cycle battery on the stereo bank.
AGMs have more resistance to vibration and shock.
Also measure the batteries at the terminals when you return to the trailer. Allow the alternator inflated charge to dissipate for 15 minutes or so before measuring. If you are not getting back to 12.7 volts for lead acid or 12.8 volts for AGM then you haven't burned enough gas for long enough to recharge the batteries. In that case you must have an AC shore Smart charger. Hopefully you have AC access when in storage.

If I remember right stock mastercraft dual battery setups in 2007 used a blue seas style switch and not a perko. Does your switch have off/on/combined or off/battery 1/battery 2/both? Where is the stereo hooked up to? Is everything electrical in the boat all hooked up to the same distribution point or is the stereo hooked to the 2nd battery and the main harness hooked to the starting battery? Again if I remember correctly mastercraft didnt' hook their batteries up as a "start" battery and a "house/stereo" battery but instead wired it as a "main" battery and a "backup" battery. Basically I think everything is probably hooked up to the switch common terminal so the following happens:

-When in the off position the batteries are completely disconnected from the start system as well as the stereo and all other possible loads. If this is the case hopefully the auto bilge is hooked directly to a battery so it works even with the switch off.
-When in the on position the stereo, starter and all other loads will be running off the 1st/main battery. Nothing is hooked to the backup battery. The backup battery isn't being discharged nor is the alternator charging it.
-When in the combined position the backup battery and main battery are hooked in parallel. This basically turns both batteries basically into one large battery.

In my opinion this isn't how I would want to wire up the boat. I would prefer to move all the stereo stuff directly to the secondary/stereo battery and leave the main harness where it is. In this format I would run the boat most of the time in the combined position. This way both batteries are receiving current from the alternator. Then if you are going to turn the boat off and listen to the stereo turn the switch to the "on" position. This will isolate the 2 batteries. The stereo will draw down the "stereo" battery while leaving you with a fully charged and ready to go "start" battery. Once you start the boat and let it run for a minute or two(to let the battery rebound/charge from the hit it took to start the boat) turn the position to the combined position so both batteries are getting charged. Then like David mentioned I would invest in an AC 2 bank charger if you have the ability to plug the charger in all/most nights. When the charger is running you could put the switch in the off or on position. You just want to make sure the 2 battery banks are separate when the charger is running.

David also gave you some good ideas on testing. I would buy a digital voltmeter. Check the batteries in the morning to make sure they are somewhere around 12.5-12.7 volts. If lower you either have batteries that are going bad or the alternator isn't keeping up with the demand and not fully charging them. Also check the battery voltage with the boat running. I believe the output of your alternator should be around 14.4 or 14.5v. You batteries should be showing that same voltage or within a tenth or so if your cables/connections are in good shape. If there is more than a couple tenths difference you are having a voltage drop that needs to be addressed because your batteries aren't seeing the full voltage/charge to be maintained.

My biggest suggestion is to do some research and find exactly how your setup is wired. Only then can you really know what to do to properly maintain it.

I just sent an email to my deka rep to find out what he suggests for high vibration. I know AGM's are recommended but I am checking to see if Deka makes a flooded battery that has a better plate design to handle high vibration. I will let you know what I hear.

Most of the battery question relate to two battery systems...a starting and a house. We have only one battery...a deep cycle Interstate group 24. It's about six years old and I'm starting to think that I should be replacing it. Our stereo is just the four in-boat speakers with a JL amp. At some point I may add a 10" sub. We don't really drive the stereo hard and it likely wouldn't be played for hours without the boat running.

The group 24 battery has been fine, but i was thinking that I should upgrade to something bigger if I plan to add a sub down the road. What would you guys recommend? The Interstate 29 seems to get some love. Any other suggestions? I don't plan to add a second battery.

endlessbreak, I would really consider a 2 battery system even if you just use it is a 2 exact same banks with everything hooked up to the switch. This way you always have a backup battery.

If you really are set on the idea of a single battery I would look at the Interstate SRM-29, Deka DP27 or Deka DP31DT. All of these are longer than your current battery so you will need a different battery box but a box is $10 or so.

Brett my 08 X2 had the original batteries in it when I sold it 4 months ago and I never did anything to them but put a charger on them in the spring. We ran the stereo a lot at the beach. I always left the battery switch on 1 and never had a problem. I don't remember what batteries were in it but maybe MC could tell you it you contact them. Maybe I just got lucky. Good luck figuring something out

It's hard to imagine that your electrical usage of your batteries is killing them. I would think it more has to do with vibration ... and ... extraordinary vibration, like hard shocks. Battery plates are usually hung from busbars by tabs along their upper edge. It's like hanging them by their necks. And battery plates are usually composites of various materials. Slamming batteries in rough water is no good.

endlessbreak, I would really consider a 2 battery system even if you just use it is a 2 exact same banks with everything hooked up to the switch. This way you always have a backup battery.

If you really are set on the idea of a single battery I would look at the Interstate SRM-29, Deka DP27 or Deka DP31DT. All of these are longer than your current battery so you will need a different battery box but a box is $10 or so.

I have 2 battery system with blue sea battery switch: For starting and when sitting around with boat not running I leave it on battery 1. Then when underway I turn to 1 + 2. This then recharges 1 and tops off battery 2. So battery 2 is totally isolated except for when it charging, and is always around in emergency to start the boat if I drain battery 1.

Additionally, I for sure know my switch is and I would guess all models are what is called make before break. So after I start the boat on switch one, I can go back and move the switch to 1 + 2 without having to turn anything on or off.

My only dilemma is that I run my weaker battery for battery 1 so once in a while I drain it pretty bad when I hang out in boat not running. But that leaves better one in reserve position. I could switch and have weaker battery for reserve and would probably never have a problem. But I don't have the nerve.

I like to replace batteries every 4 or 5 years. When I do I think I will try to get one that is a bit wider as I have some room. This would give me more amps and could still get in and out.